Physics PLEASE

I'm trying to solve this problem

Calculate (a) how long it took King Kong to fall straight down form the top of the Empire State Building (380 m high), and (b) his velocity just before "landing".

My teacher said
try and rearagne this equation for t
X = Xo + Vo t + 2^-1 a t^2

I tried to rearange it for t and i guess i did it wrong i got

t = a^-1 (2(X - Xo - Vo))

I guess i did it wrong
so could you please show me how to rearange the equation for t step by step because I guess I did it wrong thanks...

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  1. If
    X = vertical distance from Xo at time t, positive upwards, and
    Vo = velocity at t=0
    a = acceleration due to gravity, -9.81 m/s/s
    Then the proposed equation is correct.
    X = Xo + Vo t + 2^-1 a t^2

    For your particular case,
    Xo=380 m, (top of building)
    X=0 (ground)
    Vo=0 (just before the fall)
    a=-9.81 m/s/s
    That translates to

    0 = 380 + 0*t + (-9.81)t2/2

    Since the middle term "disappears" because of the coefficient of 0, then
    9.81t2/2 = 380

    from which you can find t without much ado.
    The time is a touch more than 6 seconds if air resistance and his exceptional height are ignored.

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  2. thanks

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  3. Sorry, t should be a touch less than 9 seconds, being
    sqrt(2*380/9.81)
    The 6 seconds estimate did not account for the factor of 2.

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